The development of new wind turbines has resulted in an increase in their size and power. Large wind turbines enable more capacity to be installed at the same site and reduce the visual impact of a farm consisting of several wind turbines.
A wind turbine consists of a stationary tower that elevates a nacelle bearing an electrical generator attached to a rotor mechanically. The rotor comprises a hub that attaches at least one blade, bolted to some studs from some bearings on the hub, which transforms the wind's kinetic energy in the rotating rotor.
The increase of generated power is linked directly to the dimensions of the wind turbine rotor and the consequential lengthening of the wind turbine blades. The blades represent the most critical element of a wind turbine and therefore undergo preventive inspections and corrective interventions for which the blades must be dismounted from the hub and brought down to the ground, and subsequently hoisted and remounted onto the hub after completing the maintenance tasks.
To do so, maintenance workers use large-scale cranes for handling rotors of a significant size and weight. Cranes of this sort have various drawbacks. Firstly, they are very costly, hence the cost of installing a wind turbine farm or undertaking maintenance is notably increased with their use. Secondly, given that wind turbines are usually installed on sites that are not easily accessed, transferring these cranes to the required spot is virtually impossible and normally requires conditioned accesses, which adds further complications and costs.
In this regard, the acknowledged state of the art provides various solutions that describe different pieces of equipment for mounting and dismounting wind turbine blades.
Patent WO2011/095167 describes hoisting equipment for mounting/dismounting that has a winch inside the wind turbine hub and attaches the blade through a hook to plates bolted to the blade bearing joint bolts. The equipment has an element equipped with a roller that is placed between the hook and the winch, enabling the blade to be lowered vertically and subsequently rotated to a horizontal position when near the ground. However, the drawback of this system is its need for a large amount of space to install a winch that supports the elevated weights of current blades in addition to retention and rotation-proof systems that are more reliable than the one described above.
Patent WO2009/128708 describes equipment furnished with two elements, one placed on the wind turbine hub, which grasps the blade from the bearings, and the other placed inside the blade. These elements work together to raise or lower a blade using some means of positioning and some means of lifting. The blade, secured by a winch, is lowered vertically (the tip pointing toward the ground) by engaging an actuator in one of the means that balances the blade toward a predetermined alignment with the tower. A winch is used to guarantee the vertical descent of the blade
Patent US2010/0253086 describes a system that incorporates some pulleys outside the hub, in the spaces existing between the blades, that are used for guiding a cable connected with a service crane located on the wind turbine nacelle or winch (W) installed on the ground. The blade is secured for lowering or raising by a pulley inside the hub.
In view of the drawbacks of the aforementioned solutions, a need is thus envisioned for implementing a solution that could guarantee the mounting and/or dismounting the blades at a minimum cost.